- A
Implement a retry mechanism in the Lambda function to check object existence before processing.
Retry handles eventual consistency.
- B
Use S3 Transfer Acceleration.
Why wrong: Transfer Acceleration is for upload speed.
- C
Configure the S3 event notification to trigger only when objects with a specific suffix are created.
Can target files that are written last (e.g., .tmp).
- D
Use an Amazon SQS queue to buffer the S3 events.
Why wrong: SQS doesn't wait for object completion.
- E
Increase the Lambda function timeout.
Why wrong: Timeout doesn't affect object write completion.
Question 85 of 1,616
Handling S3 Eventual Consistency in Lambda
This DVA-C02 practice question tests your understanding of development with aws services. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A developer is troubleshooting an AWS Lambda function that is invoked by an Amazon S3 bucket notification. The function processes new objects but sometimes fails because the object is not fully written before Lambda reads it. Which TWO actions can the developer take to fix this?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Implement a retry mechanism in the Lambda function to check object existence before processing.
Option A is correct because implementing a retry mechanism with a check for object existence (e.g., using S3 HeadObject API) allows the Lambda function to verify that the object is fully written and consistent before processing. This handles the eventual consistency model of S3 for new PUTs, where the object may not be immediately available after the notification is sent.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Implement a retry mechanism in the Lambda function to check object existence before processing.
Why this is correct
Retry handles eventual consistency.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use S3 Transfer Acceleration.
Why it's wrong here
Transfer Acceleration is for upload speed.
- ✓
Configure the S3 event notification to trigger only when objects with a specific suffix are created.
Why this is correct
Can target files that are written last (e.g., .tmp).
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use an Amazon SQS queue to buffer the S3 events.
Why it's wrong here
SQS doesn't wait for object completion.
- ✗
Increase the Lambda function timeout.
Why it's wrong here
Timeout doesn't affect object write completion.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse S3's eventual consistency model with network or timeout issues, leading them to choose SQS buffering or increasing timeout instead of addressing the root cause with a retry and existence check.
Detailed technical explanation
How to think about this question
Amazon S3 provides read-after-write consistency for new PUTs of objects, but the event notification is sent asynchronously and may arrive before the object is fully replicated across all S3 infrastructure. A retry mechanism with exponential backoff and a HeadObject check ensures the function waits until the object metadata confirms it is present and has the expected size, which is critical for applications like image processing or data ingestion where partial reads cause failures.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
What to study next
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FAQ
Questions learners often ask
What does this DVA-C02 question test?
Development with AWS Services — This question tests Development with AWS Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Implement a retry mechanism in the Lambda function to check object existence before processing. — Option A is correct because implementing a retry mechanism with a check for object existence (e.g., using S3 HeadObject API) allows the Lambda function to verify that the object is fully written and consistent before processing. This handles the eventual consistency model of S3 for new PUTs, where the object may not be immediately available after the notification is sent.
What should I do if I get this DVA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
This DVA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DVA-C02 exam.
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